For fastening and joining bearing elements, particularly nose pads, to the frame of glasses, a common practice is to provide thin, suitably bent lengths of wire that have a hardness of 120 to 200 DPN (Vickers diamond pyramid hardness number), each wire being soldered on one end to the frame around one lens and on the other being fastened to a holder or other receptacle for connection to a bearing element, such as a nose pad. The construction of this kind of holder, in terms of its shape and operation, is intrinsically determined by the type of bearing element, and a number of designs are known.
The rigidity of each wire makes the support arms practically inflexible, so the optician must adapt them to the anatomical characteristics of the area of the glasses wearer's nose which is to be contacted by each nose pad. Because of the rigidity of the wires, they, and the nose pads, then remain in the position set by the optician. In this position, hereinafter called the normal position, the applicable weight components of the glasses frame are then transmitted to the sides of the nose, via the support arms and the nose pads.
However, situations do exist in which the rigidity of the support arms, however desirable it may be for the sake of basic stability, is nevertheless a great disadvantage; not only are the support arms unable to adapt to anatomical changes, but they also have an unsatisfactory effect if a sudden, pulse-like pressure is exerted on the glasses, such as if a ball hits the glasses during athletic activity. In that case, the support arm, because of its rigidity, will not yield until a certain pressure level is reached; this may be quite painful for the glasses wearer, because all the external force exerted is then transmitted, substantially unattenuated, to the sides of the nose via the nose pads.
Given the relatively small bearing area of the nose pads, and if the incident force is in such a direction as to cause possible harm, the result will at least be severe pain to the glasses wearer, and possibly even skin injuries.
If the severity of such a sudden strain exceeds a certain limit value, the support arm bends; in that case, although some of the arriving energy is absorbed by the bending of the support arm, nevertheless the arm then remains in the deformed, bent position; the glasses are no longer correctly seated and must be readjusted by the optician, and sometimes the deformation is so great that this is no longer possible.